1. Field of Invention
This invention relates to control of blood flow in an arterial bloodline utilized to return blood to the aorta or femoral artery of a patient being supported on a heart-lung machine as part of a cardiopulmonary bypass procedure. More specifically, the present invention relates to a device and method for preventing aspiration of air through sutures into the natural aorta or femoral artery by reason of a siphoning effect within the blood line when the associated pump returning the blood becomes defective or inoperable.
2. Prior Art
It is estimated that over 300,000 cardiopulmonary bypass operations are performed annually within the United States alone. This procedure is illustrated in FIG. 1 wherein the patient's circulatory system 10 is linked to a heart-lung machine 11 which includes an oxygenation unit 12 and pumping device 13. Blood is sucked from the superior and inferior vena cava 14 through venous cannulae 15 and 16. This blood is oxygenated in the artificial lung 12 and is pumped back to the circulatory system by pump 13 through an arterial blood line 17 feeding into the patient's aorta. Although the pump 13 is shown following the oxygenator 12, current trend is to position this pump in the circuit preceding the oxygenator, as illustrated in the configuration of FIG. 2.
For many years, the blood pump 13 utilized in the bypass procedure was a roller-pump design wherein the arterial blood line 17 was occluded by the pumping members. In approximately 1984-85, nonocclusive pumps were introduced and have since gained increasing favor as part of the bypass procedure. Currently, approximately 20% of the 300,000 cardiopulmonary bypass operations are serviced by non-occlusive pumps which incorporate structure similar to a rotary member such as used in the Biomedicus Pump (TM).
Although the rotary pump offers many advantages over prior occlusive pumps, the nonocclusive nature of the rotary pump poses a structural deficiency which may have serious repercussions on a patient upon malfunction or termination of pumping action of the rotor. This deficiency is illustrated in FIG. 2 wherein the respective venus cannulae 15 and 16 are graphically illustrated in the conventional attachment configuration for transferring blood to the pump 13. This pump 13 and attached oxygenator 12 are typically positioned under the patient 20 to facilitate gravity flow of blood from the patient to the pump and oxygenator system.
This configuration develops a column of blood of approximately 120 centimeters in height as illustrated by distance arrow 21. This is equivalent to fluid pressure of approximately 90 millimeters of mercury.
The pump 13 serves to overcome this pressure and return blood through the arterial blood line 17 to a femoral artery 18 for delivery to a femoral artery or to the aorta. If the pump 13 fails to supply enough pumping force to overcome the fluid pressure of the blood, the effect of gravity causes reverse flow of the blood in the arterial blood line 17 and develops a siphoning effect as blood flows back into the pump 13/oxygenator 12.
As a consequence, a subatmospheric pressure is created in the femoral artery or aorta such that air can be aspirated through suture lines or from other sources. This air then accumulates in the aorta and in the associated arterial blood line. In such an emergency situation, the attention of the perfusionist may be directed toward the failing pump and he may forget to clamp the arterial blood line tube 17. If the pump is then started, the perfusionist may transmit air from the tubing into the aorta. Even worse, concealed air within the aorta may pass into the patient's circulatory system causing an air embolism. Such occurrences have proved fatal for a number of patients.
The fact that the arterial blood line 17 is typically transparent does not always give adequate early visual warning to the perfusionist upon occurrence of such pump failure. Much of the upper transparent blood line 17 is concealed under patient covers, blocking view of entrained air. It will be noted that detection of air within the lower arterial blood line means that air has already been siphoned into the aorta (not visible to the perfusionist). Under current procedures, the perfusionist is responsible to monitor against such pump failure and siphoning of blood. Typically, the perfusionist must mechanically clamp the arterial blood line 17 upon detection of pump failure and then evaluate the extent of potential aspiration of air within the circulatory system. Detection of any air requires correction before reinstating blood flow, thereby creating a further life threatening situation.